Actor Michael Douglas arrives for the screening of Wall Street - Money Never Sleeps presented out of competition at the 63rd Cannes Film Festival on May 14, 2010 in Cannes.Photo: FRANCOIS GUILLOT/AFP/Getty Images/Files

Rates of throat and anal cancer linked to one of the most common sexually transmitted infections in Canada are increasing in younger men and women at a disturbing rate, according to new Alberta research spanning 35 years.

The study shows that the incidence of human papillomavirus, or HPV-related oropharyngeal cancers — tumours at the base of the tongue and tonsils — increased among both males and females between 1975 and 2009. The increase among men was double that among women.

Among women, the incidence of anal cancer doubled over the study period.

The research confirms what others have found, that HPV-related cervical cancer is falling, largely due to widespread Pap smear screening.

But the increases in cancers of the throat and anus are “disturbing,” given that no screening programs exist to detect either of these cancers early, the authors write in the journal CMAJ Open.

The researchers say female-only HPV vaccination programs should be expanded to include males as well.

In 2008, Alberta began offering free HPV vaccine to all girls starting Grade 5, with a three-year catch-up program for Grade 9 girls. Starting in September, the program will be offered to all Grade 5 boys, with a four-year catch-up program for Grade 9 boys.

Expanding the programs to males is expected to prevent 440 cases of head and neck cancer in Alberta men, according to the province’s health ministry.

Other provinces are weighing expanding HPV to boys.

An estimated 75 per cent of sexually active men and women will have at least one HPV infection in their lifetime, according to the Public Health Agency of Canada.

Most people with healthy immune systems clear HPV from their bodies, and only a small proportion will develop cancer. Still, HPV is believed responsible for about five per cent of all cancers.

The virus has been known for decades to cause cervical cancer, but evidence has only recently begun to mount linking HPV to other cancers as well, including cancers of the anus, penis, vagina and oropharynx, the team writes.

“The increasing incidence of these HPV-related cancers has been attributed to changes in lifestyle-related risk factors, most notably sexual behavior.”

Actor Michael Douglas touched off a media storm last year when he suggested in an interview with The Guardian newspaper that he developed throat cancer from the HPV virus by performing oral sex on women. He later said he actually had tongue cancer but lied about it as it would involve radical surgery and he didn’t want to cancel the tour for his Wall Street movie sequel.

For their study, the Calgary researchers used the Alberta Cancer Registry to identify cancers associated with HPV diagnosed between January 1975 and December 2009.

Overall, 8,120 HPV-related cancers were diagnosed over the study period. Most were cervical cancer (56 per cent) and oropharyngeal cancer (18 per cent).

Oropharyngeal cancers increased for each five-year interval of the study period among men, increasing from 1.2 to 3.7 per 100,000 over the study period. The highest increase in men was in those under 45.

Anal cancer in women doubled, from 0.7 to 1.5 per 100,000 people.

The increases aren’t dramatic, but they are worrisome, the researchers said, especially because they’re occurring in younger age groups. Treatment for cancers of the oral cavity can affect a person’s speech and ability to swallow.

Smoking and alcohol use have historically caused throat cancer, but recent research is now implicating HPV as a significant cause. In a study published last year, researchers from Western University and the Lawson Health Research Institute in London, Ont. detected HPV in more than half (57 per cent) of 160 cases of tonsillar cancer studied.

“HPV is not the cause of all head and neck cancers, and certainly not all anal cancers, but it certainly increases the risk,” said Lorraine Shack, an assistant professor in the Cumming School of Medicine at the University of Calgary and lead author of the new study.

Because her team looked at long-term trends over time, “we don’t have data specifically about who was infected or who wasn’t,” Shack said. “But HPV is strongly associated with these cancers that we looked at.”

The findings also mirror data coming out of other provinces, including B.C.

It will likely take decades for school-based HPV vaccination programs to have an impact, Shack said. But the majority of women are exposed by the time they’re 25, “which is why it’s recommended you get vaccinated at a younger age.”

The risk of cancer increases with age, meaning the findings may be an early sign “of a bigger problem coming forward,” Shack added.